Problem: $ { {3} \times \left[\begin{array}{rrr}{1} & {-2} & {-1} \\ {-1} & {-1} & {4}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{3}\times{1} & {3}\times{-2} & {3}\times{-1} \\ {3}\times{-1} & {3}\times{-1} & {3}\times{4}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{3} & {-6} & {-3} \\ {-3} & {-3} & {12}\end{array}\right]}$